Regulatory Capital (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Retained earnings	$ 16,233	$ 16,049
Capital ratio: required common equity tier 1 capital	5.50%	4.50%
Capital ratio: required tier 1 capital	7.00%	6.00%
Capital ratio: required total capital	9.00%	8.00%
Capital ratio: required tier 1 leverage	4.00%	4.00%
Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,243	$ 10,250
Retained earnings	16,233	16,049
Accumulated other comprehensive income (loss)	(1,020)	(1,422)
Treasury stock, at cost	(6,719)	(6,457)
Total	18,737	18,420
Goodwill and other intangible assets, net of associated deferred tax liabilities	(6,242)	(5,927)
Other adjustments	(91)	(60)
Common equity tier 1 capital	12,404	12,433
Preferred stock	2,703	2,703
Trust preferred capital securities subject to phase-out from tier 1 capital	0	237
Other adjustments	(75)	(109)
Tier 1 capital	15,032	15,264
Qualifying subordinated long-term debt	1,259	1,358
Trust preferred capital securities phased out of tier 1 capital	890	713
ALLL and other	9	12
Other adjustments	1	2
Total capital	17,191	17,349
Credit risk	52,865	51,733
Operational risk	44,231	43,882
Market risk	3,537	3,937
Total risk-weighted assets	100,633	99,552
Adjusted quarterly average assets	$ 217,029	$ 221,880
Common equity tier 1 capital	12.30%	12.50%
Tier 1 capital	14.90%	15.30%
Total capital	17.10%	17.40%
Tier 1 leveraged	6.90%	6.90%
Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,243	$ 10,250
Retained earnings	16,233	16,049
Accumulated other comprehensive income (loss)	(1,020)	(1,422)
Treasury stock, at cost	(6,719)	(6,457)
Total	18,737	18,420
Goodwill and other intangible assets, net of associated deferred tax liabilities	(6,242)	(5,927)
Other adjustments	(91)	(60)
Common equity tier 1 capital	12,404	12,433
Preferred stock	2,703	2,703
Trust preferred capital securities subject to phase-out from tier 1 capital	0	237
Other adjustments	(75)	(109)
Tier 1 capital	15,032	15,264
Qualifying subordinated long-term debt	1,259	1,358
Trust preferred capital securities phased out of tier 1 capital	890	713
ALLL and other	66	66
Other adjustments	1	2
Total capital	17,248	17,403
Credit risk	98,133	93,515
Market risk	1,484	2,378
Total risk-weighted assets	99,617	95,893
Adjusted quarterly average assets	$ 217,029	$ 221,880
Common equity tier 1 capital	12.50%	13.00%
Tier 1 capital	15.10%	15.90%
Total capital	17.30%	18.10%
Tier 1 leveraged	6.90%	6.90%
State Street Bank | Basel III Advanced Approaches
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,941	$ 10,938
Retained earnings	10,997	10,655
Accumulated other comprehensive income (loss)	(841)	(1,230)
Treasury stock, at cost	0	0
Total	21,097	20,363
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,938)	(5,631)
Other adjustments	(88)	(85)
Common equity tier 1 capital	15,071	14,647
Preferred stock	0	0
Trust preferred capital securities subject to phase-out from tier 1 capital	0	0
Other adjustments	0	0
Tier 1 capital	15,071	14,647
Qualifying subordinated long-term debt	1,271	1,371
Trust preferred capital securities phased out of tier 1 capital	0	0
ALLL and other	5	8
Other adjustments	0	0
Total capital	16,347	16,026
Credit risk	48,489	47,677
Operational risk	43,663	43,324
Market risk	3,523	3,939
Total risk-weighted assets	95,675	94,940
Adjusted quarterly average assets	$ 212,843	$ 217,358
Common equity tier 1 capital	15.80%	15.40%
Tier 1 capital	15.80%	15.40%
Total capital	17.10%	16.90%
Tier 1 leveraged	7.10%	6.70%
State Street Bank | Basel III Standardized Approach
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common stock and related surplus	$ 10,941	$ 10,938
Retained earnings	10,997	10,655
Accumulated other comprehensive income (loss)	(841)	(1,230)
Treasury stock, at cost	0	0
Total	21,097	20,363
Goodwill and other intangible assets, net of associated deferred tax liabilities	(5,938)	(5,631)
Other adjustments	(88)	(85)
Common equity tier 1 capital	15,071	14,647
Preferred stock	0	0
Trust preferred capital securities subject to phase-out from tier 1 capital	0	0
Other adjustments	0	0
Tier 1 capital	15,071	14,647
Qualifying subordinated long-term debt	1,271	1,371
Trust preferred capital securities phased out of tier 1 capital	0	0
ALLL and other	66	66
Other adjustments	0	0
Total capital	16,408	16,084
Credit risk	93,520	89,164
Market risk	1,484	2,378
Total risk-weighted assets	95,004	91,542
Adjusted quarterly average assets	$ 212,843	$ 217,358
Common equity tier 1 capital	15.90%	16.00%
Tier 1 capital	15.90%	16.00%
Total capital	17.30%	17.60%
Tier 1 leveraged	7.10%	6.70%